Ethylene-acrylic acid polymers having improved optical characteristics

ABSTRACT

A FRACTIONAL PRECIPITATION PROCESS IS EMPLOYED TO SUBSTANTIALLY IMPROVE THE OPTICAL PROPERTIES OF ETHYLENEACRYLIC ACID POLYMERS.

United States Patent 3 814,737 ETHYLENE-ACRYLICACID POLYMERS HAVINGIMPROVED OPTICAL CHARACTERISTICS Ronald E. Gilbert, Orange, Tex., JosephW. Jones, Jr., Leawood, Kans., and Raymond M. Henry, Gibsonia, Pa.,assignors to Gulf Research & Development Company, Pittsburgh, Pa.

N 0 Drawing. Continuation-impart of application Ser. No. 77,027, Sept.30, 1970. This application Aug. 14, 1972, Ser. No. 280,250

Int. Cl. C08f 15/02 US. Cl. 26080.73 2 Claims ABSTRACT OF THE DISCLOSUREA fractional precipitation process is employed to substantially improvethe optical properties of ethyleneacrylic acid polymers.

REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of our copending application, Ser. No. 77,027,filed Sept. 30, 1970, now abandoned.

BACKGROUND OF INVENTION Ethylene-acrylic acid polymers have been foundto be of particular value in the preparation of laminated glassstructures which are employed as safety glass in automobiles and in theconstruction of buildings. It 'will be appreciated that in theconstruction of such laminated glass structures that theethylene-acrylic acid polymer employed as an inner layer must have verygood optical characteristics. For example, the optical characteristicidentified as hazewhich vmeasures the frosty appearance of transmittedlight through the ethylene-acrylic acid polymermust be very low.

Ethylene-acrylic acid polymers which have been found to be particularlysuitable in the preparation of laminated glass structures are randomcopolymer of ethylene-acrylic acid and normally contain from 0.06 to 0.5mol of acrylic acid per mol of contained ethylene. Theseethylene-acrylic acid polymers can be prepared by processes such asdescribed in US. Pat. 3,485,785 and in Canadian Pat. 889,920. Laminatedglass structures prepared from such ethylene-acrylic acid copolymersnormally have a haze of 3 to 24 percent, as measured by the Gardnerhazemeter. This is contrasted to an acceptable haze reading of less than2 percent for safety glass employed in the fabrication of automobiles.

Accordingly, an object of the invention is to provide anethylene-acrylic acid polymer having improved optical characteristics.

Another object of the invention is to provide an ethylene-acrylic acidfilm having improved optical characteristics.

Yet another object of the invention is to provide a laminated glassstructure containing an ethylene-acrylic acid polymer inner layer havingsubstantially improved haze.

Other objects, advantages and features of the invention will be readilyapparent to those skilled in the art from the following description andappended claims.

3,814,737 Patented June 4, 1974 SUMMARY OF INVENTION DESCRIPTION OF THEINVENTION The invention is directed to the fractional precipitation ofrandom ethylene-acrylic acid polymers. The ethyleneacrylic acid polymerswill contain from about 0.06 to about 0.5 mol and preferably from about0.08 to about 0.25 mol of acrylic or methacrylic acid per mol ofcontained ethylene. In addition to ethylene and acrylic acid monomers,the ethylene-acrylic acid polymers may contain minor portions of one ormore additional monomers such as vinyl acetate, esters of theabove-named acids, and amides such as acrylamide and methacrylamide.

In the practice of the invention, the ethylene-acrylic acid polymer isdissolved in a solvent at an elevated temperature. Solvents which havebeen found to be particularly efiective in dissolving theethylene-acrylic acid polymer are mixed solvents such as mixtures ofxylene and acetic acid, and xylene and isopropyl alcohol. Of the namedmixed solvents, normally xylene comprises from about to percent byvolume of the mixed solvent. The solution of the ethylene-acrylic acidpolymer in the solvent is normally elfected at a temperature below theboiling point of the solvent but above C. with even higher solutiontemperatures preferred to shorten the time required to place the polymerin solution.

After solution of the ethylene polymer has been completed, a nonsolventcan be added to the solution and the admixture permitted to cool toambient temperature. A precipitate is formed which can be separated fromthe liquid medium by filtration. Infra-red analysis of the materialremoved by precipitation and filtration shows a strong 13.7n band,indicating that at least a substantial portion of the material removedis highly crystalline. I

The nonsolvent found to be particularly effective in the practice of theinvention is Cellosolve. Other suitable nonsolvents include the glycolssuch as ethylene and propylene glycol. Generally, the volume ofnonsolvent added to the polymer solution will range from 0.5 to 10percent by volume of the polymer solution.

After the first formed precipitate has been separated from the liquidmedium, a precipitating agent for the ethylene-acrylic acid polymer canbe added to the polymer solution. Suitable precipitating agents includeall alcohols such as methanol, ethanol, propanol and butanol and the lowmolecular weight ketones such as acetone and methyl ethyl ketone.Normally, the volume of precipitating agent employed in the secondprecipitation step will range from 50 percent to a volume equal to thevolume of the polymer solvent.

The precipitated ethylene-acrylic acid polymer can be separated from thesolvent by conventional means such as filtration. The recovered polymerwhen cast into a film by conventional processes has substantiallysuperior haze characteristics when compared with the hazecharacteristics of ethylene-acrylic acid polymer films prepared byconventional processes. The term haze refers to that percentage oftransmitted light which in passing through the specimen deviates fromthe incident beam by forward scattering. Only light flux deviating morethan 2.5 degrees on the average is considered to be haze. As employed inthis application, the haze test results refer to those results obtainedby employing American Society for Testing and Materials (ASTM) TestMethod D 1006-61. Infra-red analysis of the ethylene-acrylic acidpolymer product produced by the fractional precipitation process of theinvention shows the absence of a band at 13.7,u. and thus the absence ofcrystalline material from the polymer product.

The ethylene-acrylic acid polymers of this invention are particularlyadaptable in the preparation of laminated glass structures which areemployed as safety glass in automobiles and in the construction ofbuildings. The laminated glass structures are prepared by bondingtogether at least two glass laminae with the ethylene-acrylic acidpolymer, thereby obtaining a laminated glass structure with anethylene-acrylic acid polymer film layer as the inner layer.

A film layer of the product ethylene-acrylic acid polymer can beobtained by laying down an aqueous dispersion of the polymer on asubstrate such as glass and evaporating the water therefrom or by meltextrusion of the ethylene-acrylic acid polymer employing proceduresknown to the art. Alternatively, an organic solvent solution of theethylene-acrylic acid polymer can be laid down on a surface and thesolvent evaporated therefrom.

The laminated glass structures can be prepared, for example, by placingfilms or tapes of the ethylene-acrylic acid polymer between two glasslaminae before the laminae are subjected to heat and pressure. Thelaminates thus prepared are firmly bonded together and ordinarily cannotbe separated without destroying at least one of the laminae. A filmlayer can also be obtained by distributing solid particles of theethylene acrylic acid poly mer on one lamina, placing a second lamina ontop there of, and, finally, heating the laminated structure underpressure.

The laminated glass structure containing the ethyleneacrylic acidpolymer inner layer has surprisingly high impact strength, is moreresistant to temperature change than glass laminae conventionallyemployed as safety glass in automobile Windshields, for example, and, inaddition, will by reason of this invention have optical characteristicssubstantially superior to those ethylene-acrylic acid polymer resins andother synthetic resins such as polyvinyl butyral conventionally employedin the manufacture of laminated glass structures.

It has been observed that laminated glass structures having anethylene-acrylic acid polymer prepared by the fractional precipitationprocess of this invention will have a haze of less than 2 percent, asmeasured by the Gardner hazemeter employing ASTM D 1003-61, whereaslaminated glass structures prepared employing synthetic resins known tothe art will normally have a haze of 3 to 24 percent as measured by theGardner hazemeter employing ASTM D 1003-61.

The following examples are presented to illustrate the objects andadvantages of the invention. It is not intended, however, that theinvention should be limited to the specific embodiments describedtherein.

EXAMPLE I In this example, a glass laminated structure was prepared fromglass panes measuring Me in thickness, employing an ethylene-acrylicacid copolymer inner layer wherein the concentration of acrylic acidcomonomer in the ethylene polymer was 17.5 weight percent. Theethylene-acrylic acid copolymer had been prepared by the thermaldecomposition of an ethylene-isopropyl ester of acrylic acid copolymerwith the thermal decomposition conducted in an extruder. Theethylene-acrylic acid inner film layer prepared by the melt extrusion ofan ethyleneacrylic acid copolymer had a thickness of 30 mils. Hazemeasurements of the laminated structure made on a Gardner hazemeter andemploying ASTM D 1003-61 showed that the laminated structure had a hazeof 24.1 percent.

EXAMPLE II In this example, the ethylene-acrylic acid copolymer ofExample I prepared by the thermal decomposition of theethylene-isopropyl ester of acrylic acid copolymer was dissolved in axylene-acetic acid mixed solvent to obtain a polymer solution containing2 weight percent of the ethylene-acrylic acid copolymer. The mixedsolvent comprised volume percent xylene and 15 volume percent aceticacid. The polymer solution was heated to a temperature of 130 C.

10 percent by volume (based upon the polymer solution) of Cellosolve wasadded to the solution of polymer and the resulting admixture waspermitted to cool to ambient temperature. A precipitate was separatedfrom the admixture by filtration and upon infra-red analysis showed thepresence of a strong 13.7 band.

Methanol was then added to the polymer solution so as to form a mixtureof 2 volumes of polymer solution and 1 volume of methanol. Theethylene-acrylic acid copolymer was precipitated from the solution andwas sepa rated from the liquid medium by filtration.

A glass laminated structure employing an extruded film layer of theproduct ethylene-acrylic acid polymer as an inner layer was prepared asdescribed in Example I. Haze measurements of the laminated structuremade on a Gardner hazemeter and employing ASTM D 1003-6l showed that thelaminated structure had a haze of 0.9 percent.

Comparison of the results obtained in Examples I and II demonstrates theeflectiveness of the invention to obtain an ethylene-acrylic acidcopolymer film layer having substantially improved opticalcharacteristics as determined by the measurement of haze.

Although the invention has been described with reference to specificmaterials, embodiments and details, various modifications and changes,within the scope of this invention, will be apparent to those skilled inthe art and are contemplated to be embraced in the invention.

What is claimed is:

1. A process for preparing an ethylene-acid copolymer having improvedoptical properties which consist essentially of the steps of:

( 1) Dissolving an ethylene-acid copolymer in a liquid mixed solvent ata temperature above C.,

(2) Admixing a non-solvent with the polymer solution from step (1) toprecipitate a portion of the dissolved ethylene-acid copolymer,

(3) Separating the precipitated polymer formed in step (2) andrecovering a solution containing the still dissolved portion ofethylene-acid copolymer,

(4) Adding a precipitating liquid to the polymer solution recovered fromstep (3) to precipitate the ethylene-acid copolymer, and

(5 Recovering the precipitated ethylene-acid copolymer from step (4);

the ethylene-acid copolymer employed in step (1) being a copolymerconsisting essentially of polymerized ethylene and an acid monomerselected from the group consisting of acrylic acid and methacrylic acid,said ethylene-acid copolymer containing from about 0.06 to about 0.5 molof polymerized acid monomer per mol of polymerized ethylene monomer, anyadditional monomer optionally present in the ethylene-acid copolymerbeing present in a minor portion and being selected from the groupconsisting of esters of acrylic acid, esters of methacrylic acid,acrylamide, methacrylamide and vinyl acetate; the liquid mixed solventemployed in step (1) consisting essentially of xylene and a secondsolvent selected from the group consisting of acetic acid andisopropanol; the non-solvent employed in step (2) being selected fromthe group consisting of the glycols and Cellosolve; and theprecipitating liquid employed in step (4) being selected from the groupconsisting of the 1-4 carbon alkanols, acetone and methyl ethyl ketone.

2. The process of claim 1 wherein said nonsolvent is Cellosolve.

6 References Cited UNITED STATES PATENTS 3,520,861 7/1970 Thomson et al.260-88.1 R 3,658,741 4/1972 Knutson et a1. 260-881 R 3,255,166 6/1966Bernhardt et a1. 26094.9 F 3,711,456 1/ 1973 Gilbert et al 26088.1 R

HARRY WONG, JR., Primary Examiner US. Cl. X.R.

161'-203; 26029.6 R, 31.2 R, 33.4 R, 33.6 UA, 80.8, 88.1 R

